Fasciola hepatica is a digenetic trematode which infects cattle, sheep, and humans and is distributed worldwide. The organism undergoes several dramatic morphological changes three of which occur in the mammalian host and are under investigation in my laboratory. The target of this investigation is the study of stage-specific surface components through the application of the techniques of molecular biology. Surface component coding sequences will be isolated from bacteriophage lambda expression libraries through the use of antibody probes. These cDNA coding sequences will then be used as probes to examine both the genomic location (i.e. gene clustering) and the possible stage-specific transcription of these genes. Copies of coding sequences for the genes will also be isolated from the genome along with flanking sequence in order to examine the promoters and/or enhancers involved in transcription. Very little molecular biology has been carried out on trematode parasites; hopefully this research will serve as a model system for developmental expression of surface antigens in the closely related trematode parasites Schistosoma, Paragonimus and Clonorchis. Finally, a growing body of data suggests that Fasciola, Schistosoma and Paragonimus share antigenic surface components. One such purified surface component from Fasciola has been shown to provide up to 83% protection from subsequent challenge with S. mansoni. These types of data suggest that the protein generated by the recombinant clones in this proposal may be utilized as a component of a vaccine directed generally against trematodes. Alternatively, the proteins produced by these recombinant clones may represent components specific for Fasciola and therefore useful for Fasciola diagnostic tests.